Variable resistor with tilted contact

ABSTRACT

A slide is movable lengthwise between spaced parallel collector and resistance strips. Extending across the space between the strips is a carbon block that is connected to the slide by spring means urging the block to turn on an axis parallel to the strips to press two diagonally opposite areas of the block against the strips so that the block forms a bridging contact between them.

I Umted States Patent 1111 3,603,854

[72] Inventor Mogens W. Bang [56] References Cited g y UNITED STATESPATENTS P 65333 2,976,507 3/1961 Di Girolamo et al. 338/180 1221 Med 3465 277 9/1969 Ban 338/183 Patented sept- 7,1971 g A st k l C b0 Com an3,510,821 5/1970 Eberwem et al. 338/183 [73] ssgnee e P 3,551,871 121970 Eberwein et a1. 338/183 x St. Marys, Pa.

Primary Examiner-Lewis H. Myers Assistant Examiner-D. A. ToneAttorney-Brown, Murray, Flick 8:. Peckham ABSTRACT: A slide is movablelengthwise between s aced [54] VARIQBLE RESISTOR W TILTED CONTACTparallel collector and resistance strips. Extending acro s s the 11Clams! 12 D'awmg space between the strips is a carbon block that isconnected to [52] US. Cl... 338/183 the slide by spring means urging theblock to turn on an axis [51] Int. Cl H01c 9/02 parallel to the stripsto press two diagonally opposite areas of [50] Field of Search 338/ l83, the block against the strips so that the block forms a bridgingcontact between them.

PATENTED SEP 71am sum 1 OF 2 PATENTEU SEP 719m SHEET 2 OF 2 VARIABLERESISTOR WITI-I TILTED CONTACT It is among the objects of this inventionto provide a variable resistor, in which there is a bridging contactformed from a carbon block making substantially line contact with both aresistance element and a parallel collector.

The invention is illustrated in the accompanying drawings, in which:

FIG. 1 is a side view, partly broken away, of a linear motionpotentiometer;

FIG. 2 is a fragmentary plan view and section taken on the line Il-ll ofFIG. 1;

FIG. 3 is an enlarged cross section taken on the line Illlll of FIG. 1;

FIG. 4 is a fragmentary side view of a slide with its bridging contact,showing a modification;

FIG. 5 is a cross section taken on the line VV of FIG. 4;

FIGS. 6 to 11 are views similar to FIGS. 4 and 5 of three furtherembodiments of the invention; and

FIG. 12 is a perspective view of another carbon block.

Referring to FIGS. 1 to 3 of the drawings, the long rectangular housing1 of a variable resistor, such as a potentiometer, is provided along itsfront or top with a central slot 2 extending lengthwise of the housingfor nearly its full length. Slidably mounted inthe slot for movementlengthwise of the housing is a rectangular slide 3 that has laterallyopening grooves 4 in its opposite sides receiving the sidewalls of thehousing slot to hold and guide the slide. The slide may be moved in anysuitable manner, such as by a projection or knob 5.

Inside the housing a metal collector strip 6 and an electricalresistance strip 7 are mounted against its opposite sides in parallelrelation to each other. The collector strip is provided with an integralterminal 8 that extends through the back or bottom of the housing, andeach end of the resistance strip is connected to another terminal 9likewise extending through the back. The slide 3 has a portion extendingbetween these two strips, from which it is spaced. This portion of theslide is an open frame 10 that is parallel, or nearly so, to thecollector and resistance strips. The frame preferably is rectangular.

Disposed inside the slide frame, but projecting from its opposite sides,is a carbon block 12. Carbon as used herein is intended to covergraphite also. The block is narrower than the space between the twostrips and is considerably longer, lengthwise of the strips, than it iswide. It may take various shapes in cross section, such as elliptical ordiamond shape,

but the simplest shape is rectangular, although the ends of the blockmay be curved transversely so that the block can fit more snugly in theframe and yet turn in it on an axis extending through the housing slot.The block may substantially engage the surrounding sidewalls of theframe to prevent loose play between the block and slide, but frictionbetween them can be reduced by providing those walls with inwardlyprojecting transverse ribs 13 that substantially engage the block.

It is a feature of this invention that two diagonally opposite areas,such as edges, of the block are pressed against the two parallel stripsby spring means, so that the block fonns a carbon bridging contactbetween the collector and the resistance element and remains pressedagainst them even as it wears, as

shown in FIG. 2. One way of applying the spring pressure to the block isto provide it with a central passage 15 that extends through it parallelto the strips. For best results, the central portion of the passage issmaller than the end portions. A coil spring 16 extends through thispassage in tight engagement with the block and has projecting ends heldby the sidewalls of the slide frame. The ends of the coil are straightand extend diametrically across it and fit in slots 17 in the slide. Thespring is originally positioned in the block in such a manner that theblock will have to be twisted or turned in the slide frame to a positionmore nearly parallel to the strips in order for the block to be insertedbetween them. When the block is released, the tendency of the spring tountwist will cause the diagonally opposite edges of the block to bepressed against the two strips. As the edges of the block wear away, thespring will continue to press the block against the strips.

Instead of a coil spring, a flat spring 20 can be used, as

shownin FIGS. 4 and 5. In this case the central portion of the passage21 through the carbon block 22 there is a slot of substantially the samethickness as the spring. The spring fits snugly in the passage slot andprojects from the oppositesides of. the block into slots 23 in the slideframe 24. The passage slot in the block is inclined to the side faces ofthe block so that when the block is inserted in the slide frame it willbe tilted or inclined to the frame and require slight rotation before itcan be inserted in the potentiometer housing.

A solid carbon block, without a passage through it, also can be used asthe bridging contact, as shown in FIGS. 6 and 7. In this case the block26 is held in its tilted position in a slide frame 27 by means of leafsprings 28 secured to opposite ends of the frame and extending inwardlyinto overlapping engagement with the diagonally opposite portions of theside faces of the block that are spaced from the resistance strip 29 andcollector strip 30. These springs may be integral with the slide frameas shown, or they may be snapped or clamped onto it. They press the freediagonally opposite edges of the block against the strips.

A different arrangement is shown in the remaining figures of thedrawings, where the slide 32 is not provided with a frame, but with apost 33 that extends between and across the collector and resistancestrips 34 and 35. This post supports a leaf spring 36 that is fastenedto a carbon block 37. One end of the spring is clamped onto the post,while the opposite end extends through a central slot 38 in the block.The projecting end of the spring is formed with reversely bent ears 39that hold the block on the spring, while at the opposite side of theblock there is a bend in the spring that prevents the block from movinginwardly along the spring. In order to insert the block between theresistance and collector strips, the block must be turned into aposition more nearly parallel to the strips. This will bend the springmore. When the block is released, the spring will tend to straighten andthereby press the diagonally opposite edges of the block against thestrips. The central portion of the spring may be reduced in width tolimit flexing mainly to that area.

If desired, as shown in FIGS. 10 and 11, the post 41 can be providedwith'a transverse slot 42 in which one end of a leaf spring 43 fitssnugly. The opposite end extends through a slot 44 in a carbon block 45.The slot is inclined to the side faces of the block. Between the blockand the post the spring has a laterally projecting U-shape portion whichgives the spring its flexibility. The tendency of this portion to openwider causes the spring to press diagonally opposite edges of the blockagainst the collector and resistance strips 47 and 48.

The carbon contact block 50 shown in FIG. 12 is similar to the one shownin FIGS. 8 and 9 and is provided with a central slot 51 so that it canbe mounted in place in the same way. The difference is that block 50 hasthree points of contact, one at one side and two at the opposite side.For this purpose one side of the block has a central projection 52 andthe opposite side has a central notch 53. Like a three-legged stool,this con tact will seat firmly against adjoining collector andresistance strips.

Since each of the contacts disclosed herein is a carbon block thatengages both strips, there is only one type of material in the bridgingcontact. This avoids an interface between dissimilar materials, such ascarbon and metal, which could cause chemical action and thus highercontact resistance.

According to the provisions of the patent statutes, l have explained theprinciple of my invention and have illustrated and described what I nowconsider to represent its best embodiment. However, I desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically illustrated anddescribed.

I claim:

l. A variable resistor comprising spaced parallel collector andresistance strips, a slide between said strips movable lengthwisethereof, a carbon block disposed in the space between the strips, theblock being narrower than said space,

and spring means connecting the slide and block and urging the block toturn on an axis parallel to the strips to press two diagonally oppositeareas of the block against the strips, whereby the block forms abridging contact.

2. A variable resistor according to claim 1, in which said slideincludes a frame spaced from said strips and containing said carbonblock.

3. A variable resistor according to claim 2, in which said spring meansare leaf springs having outer ends secured to opposite sides of saidframe and having inner ends overlapping and pressing against diagonallyopposite side portions of the carbon block to twist the block in theframe.

4. A variable resistor according to claim 2, in which the carbon blockis provided with a central passage through it extending across saidstrips, and said spring means extends through said passage in tightengagement with the block, the ends of the spring means projecting fromthe block and being secured 7. A variable resistor according to claim 1,in which said block is generally rectangular and said areas of the blockare diagonally opposite edges thereof.

8. A variable resistor according to claim 1, in which said slideincludes apost extending across said strips beside the carbon block, andsaid spring means is a leaf spring having one end secured to said postand having its other end secured to the central portion of said block.

9. A variable resistor according to claim 8, in which said one end ofthe spring is wrapped around the post, and said block is provided with acentral opening receiving the other end of the spring.

10. A variable resistor according to claim 8, in which said post isprovided with a passage receiving one end of the spring, said block isprovided with a passage substantially in line with the post passage andreceiving the other end of the spring, and the spring between the postand block is provided with a laterally projecting U-shape portion.

11. A variable resistor according to claim 1, in which said contactblock is provided at one side with a central projection engaging thecollector strip and at the opposite side with a central notch to formtwo spaced points of contact with the resistance strip.

1. A variable resistor comprising spaced parallel collector andresistance strips, a slide between said strips movable lengthwisethereof, a carbon block disposed in the space between the strips, theblock being narrower than said space, and spring means connecting theslide and block and urging the block to turn on an axis parallel to thestrips to press two diagonally opposite areas of the block against thestrips, whereby the block forms a bridging contact.
 2. A variableresistor according to claim 1, in which said slide includes a framespaced from said strips and containing said carbon block.
 3. A variableresistor according to claim 2, in which said spring means are leafsprings having outer ends secured to opposite sides of said frame andhaving inner ends overlapping and pressing against diagonally oppositeside portions of the carbon block to twist the block in the frame.
 4. Avariable resistor according to claim 2, in which the carbon block isprovided with a central passage through it extending across said strips,and said spring means extends through said passage in tight engagementwith the block, the ends of the spring means projecting from the blockand being secured to opposite sides of said frame, and the spring meansbeing twisted around its axis to exert pressure against the block.
 5. Avariable resistor according to claim 2, in which said spring means is acoil spring and said frame is provided with slots receiving the ends ofthe spring.
 6. A variable resistor according to claim 2, in which saidspring means is a flat spring and said frame is provided with slotsreceiving the ends of the spring.
 7. A variable resistor according toclaim 1, in which said block is generally rectangular and said areas ofthe block are diagonally opposite edges thereof.
 8. A variable resistoraccording to claim 1, in which said slide includes a post extendingacross said strips beside the carbon block, and said spring means is aleaf spring having one end secured to said post and having its other endsecured to the central portion of said block.
 9. A variable resistoraccording to claim 8, in which said one end of the spring is wrappedaround the post, and said block is provided with a central openingreceiving the other end of the spring.
 10. A variable resistor accordingto claim 8, in which said post is provided with a passage receiving oneend of the spring, said block is provided with a passage substantiallyin line with the post passage and receiving the other end of the spring,and the spring between the post and block is provided with a laterallyprojecting U-shape portion.
 11. A variable resistor according to claim1, in which said contact block is provided at one side with a centralprojection engaging the collector strip and at the opposite side with acentral notch to form two spaced points of contact with the resistancestrip.